Genetic Diversity Among Streptomyces Isolates Causing Potato Common Scab In Different Regions Of China

Potato common scab is caused by various plant-pathogenic Streptomyces spp. Although the genus is diverse and adundant in the soil, only a small percentage of the species cause plant disease. Plant-pathogenic streptomycetes have been classified into a number of species based on DNA sequence relatedness, 16S ribosomal DNA (rDNA) sequence, and phenotypic characteristics. The most widely described common scab pathogen is Streptomyces scabies, which occurs worldwidly.Severity of common scab can vary from field to field, year to year in the same field, and from cultivar to cultivar. This is due in part to variation in the environment (weather) and genetic variation related to resistance to the disease in potato cultivars. Little information is available on the contribution of genetic diversity by the pathogen.To examine genetic diversity in different regions within China, 30 pathogenic streptomycetes isolates were obtainedd from lesions on field-grown potatoes from eight provinces in China. Isolates were then classified into species based on sequence of variable regions in the 16S rDNA gene, phenotypic characterization and biochemical characteristics. Twenty-three isolates belonged to Streptomyces scabies (10 isolates), Streptomyces bobili (5 isolates), Streptomyces enissocaesilis (3 isolates) , Streptomyces diastatochromogenes (2 isolates), Streptomyces turgidiscabies (1 isolate), Streptomyces galilaeus (1 isolate) and Streptomyces setonii (1 isolate). The remaining isolates belonged to S. bobili based on phenotypic characterization, however were classified to S. galilaeus based on 16S rDNA gene.These data are consistent and we propose that the strains S. bobili,S. galilaeus,S. enissocaesilis,S.diastatochromogenes are novel pathogens causing potato scab in the world.In this survey, the isolates classified to Streptomyces scabies come from Heilongjiang, Neimenggu, Sichuan, Shandong, Gansu provinces; an isolate belonged to Streptomyces galilaeus was from Neimenggu province;the isolates belonged to Streptomyces bobili came from Hebei, Neimenggu,Shanxi provinces; the isolates which were classified to Streptomyces diastatochromogenes came from Shandong and Shaanxi provinces; there were three isolates of Shaanxi province belonged to Streptomyces enissocaesilis; an isolate of Shaanxi province belonged to Streptomyces turgidiscabies, and an isolate of Shandong province belonged to Streptomyces setonii.The results suggest that genetic diversity of potato scab pathogens in China is polymorphic, which may be helpful for population genetic study of scab-causing streptomycetes in China.